The present invention generally relates to a system and method for measuring pressure differential created by flowing fluids. More particularly, the present invention relates to a system and method for using pressure differential measurements to measure fluid flow rate and to calculate volumes of fluids passing through a pipeline inexpensively and accurately.
Using integrated circuit technology to bring cheap and efficient solutions to problems in developing countries helps assist philanthropic and government organizations around the world that are building schools, clinics, or homes for poor families. For example, using integrated circuit technology and electronics to develop a low cost off-grid solar water heating system has allowed digital monitoring of a number of inputs such as water temperature and controlled switch pumps to optimally move water according to thermodynamics principles. In dry regions of the world, water is a major concern in terms of both efficient usage and the cost of building, monitoring and maintaining a water distribution system. Monitoring water usage remotely and electronically in real time in these regions is important for distribution and billing purposes and eliminates the need for an individual to report readings periodically. The ability to build an accurate, reliable, and inexpensive electronic device with no mechanical moving parts compatible with water delivery and storage systems in developing countries is desirable.
Prior art systems allow a user to measure fluid flow rate and volume using pressure differential created by flowing fluids. For example, in Columns 4-5, Paragraphs 0067-0068, Wang et. al., U.S. Pat. Appl. No. 2009/0221986A1, describe a system for delivering medical fluids to a patient using a flow sensor module which monitors fluid pressure differential across a flow restrictor downstream of a flow valve. As further described in Column 6, Paragraphs 0078-0079, the flow sensor module includes both a flow restrictor and a differential pressure sensor that directly or indirectly measures pressure differential.
As another example, Wiklund et. al., U.S. Pat. No. 6,725,731, describe a system to measure differential pressure created by flowing fluids. As described in Columns 3-4, a flow restriction member is placed inside a pipe and a differential pressure sensor is embedded in said flow restriction member. In the embodiments described in Columns 3-4, a pressure drop is created by the flow restriction member and this pressure drop is sensed by the embedded pressure sensor. Furthermore, a separate temperature sensor is placed in the pipeline as well as a static pressure sensor as described in Column 5. Another embodiment of the system described by in Column 7 and FIG. 14 allows a differential pressure sensor to be proximate to the exterior of a flow sensor by configuring a flow restriction member such that flow is constricted in the pipe by narrowing the walls of the pipeline toward the center of the pipe and placing ports on either side of this constricted portion.
Another example of a technique to measure flow rate of fluids using pressure differential is described by Wiklund et. al., U.S. Pat. No. 5,817,950. As described in Columns 3-4 and FIGS. 1A-1C, an averaging pitot tube having a plurality of openings on a forward-facing and backward-facing surface is used to average pressure measurements taken across the entire flow of fluid or gas in a pipe. To adjust fluid flow calculations for temperature changes in the fluid flowing in a pipe, a separate resistive temperature device is positioned downstream from the averaging pitot tube, as described in Column 3 and FIG. 1A.
Another example of using pressure differential to measure velocity of flowing fluids is described by Amir et. al., U.S. Pat. No. 3,678,754. One embodiment of the device disclosed in Amir et. al. described in Column 1, relies on the use of a plate orifice placed inside a pipe where fluid is flowing to create pressure differences at two separate measuring taps along the pipeline. A separate embodiment, described in Columns 2-3, relies on a concentric or double pitot tube placed in a single location in the pipeline to create pressure measurements that move a piston inside a cylinder. The movements of this piston reflect pressure differential measurements that are recorded either using a pen making a trace on paper, or by visually noting how far the piston moves relative to etchings on the glass column in which a piston moves, as described in as described in Column 2. As described in Column 3, the device is limited to detection of fluid flow rates of 0.36 liters per hour.
The prior art systems for measuring fluid flow rate and volume using pressure differential have several disadvantages. First, the systems of Wang et. al., Wiklund et. al. ('731), and Amir et. al. require that a flow restriction is placed on the fluid that is flowing inside a pipe or tubing to generate a differential pressure. The systems of Wang et. al. and Wiklund et. al. ('950) further require that a separate temperature measurement be taken to allow a user to obtain accurate fluid flow information.
Next, the systems of Wiklund et. al. ('950) require that an averaging pitot tube be placed across the entire flow space of a pipe or tubing and require that a user place the plurality of openings in the averaging pitot tube at specific distances relative to the exterior and center of the pipe carrying a flowing fluid. Because the averaging pitot tubes employed by Wiklund et. al. ('950) cross the entire diameter of the pipe through which fluid flows, they necessarily restrict fluid flow. Furthermore, because these systems utilize averaging pitot tubes with different shapes and sizes, they must be calibrated to the particular shape and size of the averaging pitot tube, must rely on a separate temperature measurements, and must include an estimate of the static pressure to be accurate.
Finally, the device of Amir et. al. requires that mechanical moving parts be employed to allows the measurement of pressure differential. Furthermore, the device of Amir et. al. requires that measurements be recorded with paper or by visualizing movement of a piston relative to glass etchings on the outside of a cylinder.